Nanopatterning is a technique in which charged nanoparticles are deposited at desired locations under selective control to produce micro- and nano-sized structures. Nanopatterning is expected to be useful in the development of quantum devices and nano bio devices that will play leading roles in next-generation industries.
As an example of such techniques for patterning charged nanoparticles, a method is known in which a substrate is charged using an electron or ion beam, followed by deposition of oppositely charged nanoparticles. However, this method is time-consuming because the substrate is charged in a series mode. Since the substrate surface is charged using an electron or ion beam, the substrate is required to be non-conductive.
Another technique is known in which a photoresist is formed on a support and is patterned by a suitable process such as photolithography, and then only charged nanoparticles are induced into and deposited on the pattern using an electrostatic force without an ion accumulation process. This technique enables patterning of high-purity nanoparticles prepared in the vapor state but does not accumulate ions on the photoresist pattern, leaving a considerable number of nanoparticles deposited at undesired locations, i.e. on the photoresist surface, as well as on the electrically conducting substrate.
Among many vapor-phase synthesis methods, spark discharge is an efficient method for preparing nano-sized particles. Spark discharge generates a charged aerosol using a simple system, thus being useful for the assembly of nanostructures. There have been various types of methods for spark discharge. The most widely used rod-to-rod type has recently been employed for the synthesis of bimetallic or mixed-metal nanoparticles or the growth of nanowires. Spark discharge generators are known to generate nano-sized particles. However, charged aerosols having a size of 10 nm or less tend to cause electrostatic aggregation of bipolar nanoparticles. To prevent such aggregation of nanoparticles and to generate smaller-sized charged aerosols are essential in the use of spark discharge generators.
There are known methods for reducing the aggregation of particles in spark discharge generators by varying operational parameters such as spark frequency, spark energy, and carrier gas flow.
In such an effort, the present applicant has proposed a method for producing a two- or three-dimensionally shaped nanoparticle structure by focused patterning of nanoparticles (see Korean Patent Publication No. 10-2009-0089787, which was published on Aug. 24, 2009). According to this method, bipolar-charged nanoparticles and ions generated simultaneously by spark discharge of a pin-to-plate or tip-to-plate type electrode structure are fed into a reactor accommodating a patterned substrate, and an electric field is applied thereto to efficiently produce a two- or three-dimensionally shaped nanoparticle structure irrespective of the polarity of the nanoparticles or ions.
The pin-to-plate or tip-to-plate structure has an asymmetric structure consisting of a pin having a sharp tip, as an anode, and a ground plate having a central outlet. It is known that a charged aerosol generated by the pin-to-plate structure has a much smaller particle size, less aggregates, and has a narrower particle diameter distribution than that generated by a rod-to-rod structure.
However, pin-to-plate structures reported to date can form nanostructures only on limited areas, for example, areas having a diameter of about 8 mm or less. There is thus a need to develop a pin-to-plate structure that can form nanostructures on a large-area surface at a high speed for industrial application.